1. Field of the Invention
The present invention relates to a semiconductor package including a non-conductive adhesive tape, and a manufacturing method and apparatus for die bonding of the package.
2. Description of the Related Arts
In manufacture of semiconductor devices, die bonding refers to a step of attaching a semiconductor die to a substrate such as a lead frame or a printed circuit board using an adhesive. A typical adhesive used in the die bonding is Ag-epoxy which is electrically conductive. However, in a specific case, an electrically insulating (non-conductive) adhesive may be used for die bonding. For example, where multiple dies are bonded to a single substrate, a non-conductive adhesive is used for electrically insulating each individual die from others.
Most non-conductive adhesives are of a liquid type. The liquid non-conductive adhesive spreads out when the semiconductor chip is pressed for bonding, and thus the adhesive layer is very thin after the bonding, and the insulating capacity of the adhesive layer is correspondingly poor. In addition, liquid type adhesives are prone to produce voids within the adhesive layer. The voids within the adhesive layer provide a source of package cracking, such as a delamination between the adhesive layer and the substrate. Moreover, overspreading of the liquid adhesive onto the chip can cause a problem in a subsequent wire bonding.
To avoid the low insulating capability of the liquid non-conductive adhesive, an insulating film, which is made of an insulating material such as a ceramic or an epoxy, can be inserted in the adhesive layer. While the insertion of an insulating film can effectively increase the insulating capability of the adhesive layer, the die bonding process becomes complicated resulting in a manufacturing cost increase.
FIG. 1 illustrates a configuration of a semiconductor package 10 using an insulating film 15. In FIG. 1, a first semiconductor chip 13 is bonded to a lead frame 11 by a conductive adhesive 12, and a second semiconductor chip 17 is bonded to lead frame 11 using insulating film 15 so that first chip 13 is electrically insulated from second chip 17. To bond first chip 13 lead frame 11, a conductive liquid adhesive 12 is dispensed on lead frame 11, first chip 13 is placed on and pressed into dispensed adhesive 12, and adhesive 12 is cured. In contrast, die bonding of second chip 17 requires several steps. Initially, a non-conductive liquid adhesive 14 is dispensed on lead frame 11, insulating film 15 is placed on and pressed into dispensed non-conductive liquid adhesive 14, and adhesive 14 is cured. Then, an non-conductive liquid adhesive 16 is dispensed on insulating film 15, second chip 17 is placed on and pressed into the dispensed adhesive 16, and adhesive 16 is cured.
As described above, the die bonding method using an insulating film requires additional process steps for inserting the insulating film. In addition, since the method uses liquid adhesive twice, the problems associated with liquid adhesives may be doubled.
A semiconductor package in accordance with an embodiment of the present invention includes a first semiconductor chip which is bonded to a substrate, such as a lead frame, by a conductive adhesive, and a second semiconductor chip which is bonded to the substrate by a non-conductive adhesive tape. In one embodiment, the non-conductive adhesive tape includes a polyimide tape and adhesive layers on top and bottom surfaces of the polyimide tape. The polyimide tape is typically about 20 to 60 xcexcm thick, and each of the adhesive layers is typically about 10 to 30 xcexcm thick. A non-conductive adhesive tape with this construction has a dielectric strength (or breakdown voltage) of more than 2,500 V.
Another embodiment of the present invention provides a die bonding method. The method includes preparing a substrate on which a first semiconductor chip is bonded by a conductive adhesive, preparing a non-conductive adhesive tape, attaching the non-conductive adhesive tape to the substrate, and bonding a second semiconductor chip to the non-conductive adhesive tape. Preparing the non-conductive adhesive tape includes spooling a base non-conductive adhesive tape onto a reel, and cutting the base non-conductive adhesive tape, which is spooled off the reel, to a size for bonding the second chip. When attaching the conductive adhesive tape and the second chip, a temperature of approximately 150xc2x0 C. to 500xc2x0 C. is applied to the substrate, and a pressure of approximately 100 gf/mm2 (grams force/millimeter) to 600 gf/mm2 is applied to the second chip.
The invention also provides an apparatus for die bonding. The apparatus includes a stacker for loading a substrate, a transferring means for transferring the substrate, a tape provider that provides adhesive tape for bonding a second semiconductor chip to the substrate, a tape pick-up tool which transports the adhesive tape from the tape provider to the substrate, a chip provider in which the chip is placed, and a die pick-up tool which picks up the chip from the chip provider and bonds the chip to the adhesive tape on the substrate. The tape provider of the apparatus includes a reel to which the adhesive tape is spooled, a tape cutter for cutting the adhesive tape to a size for the chip, a roller for providing the adhesive tape to the tape cutter, and a tape holder for holding the adhesive tape during the cutting.